I have detected, cloned, and sequenced naturally occurring products of interchromosomal recombination between gamma (gamma-) and delta (delta-) T cell receptor (TCR) genes by polymerase chain reaction (PCR) DNA amplification. These chimeric gene rearrangements (trans-rearrangements), which have the general structures Vgamma-(Ddelta)-Jdelta and Vdelta-Jgamma, are present in normal human thymus at frequencies of greater than 10-4 and in normal human peripheral lymphoid tissues at frequencies greater than 10- 5. Many of the cloned rearrangements show potentially protein-coding open reading frames, and blot hybridization of RNA PCR reaction products suggests the presence of chimeric Vgamma-Cdelta transcripts. I have found that these gamma-delta trans-rearrangements are also present in mouse thymus. As primary objectives I propose to explore both the functional consequence of chimeric gene rearrangements and the mechanism of their occurrence. Strategies for the construction of clonal murine lymphocyte cell lines bearing and expressing trans-rearrangements are outlined. The availability of clonal lines will facilitate studies of the functional properties of predicted chimeric Vgamma-Cdelta and Vdelta-Cgamma TCR proteins. The mechanism of trans-rearrangement in developing murine thymocytes will be investigated by analysis of hypothetical circular DNA excision products and potential intermediate DNa structures. An additional objective is the detection and characterization of Vgamma-Jalpha chimeric rearrangements, theoretically predicted to derive form Vgamma-(Ddelta)- Jdelta rearrangements during thymocyte maturation, and other hypothetical chimeric TCR rearrangements such as Vbeta-Jalpha, Vgamma-(Dbeta)-Jbeta and their corresponding reciprocal products.